1. Field of the Invention
The present invention relates generally to defect inspection systems, and specifically to such defect inspection systems that utilize a television camera.
2. Description of the Prior Art
In the prior art defect inspection systems that utilize television cameras or the like, there is an inevitable, non-detectable or inspectable fault due to the characteristics of the television camera. Such conventional examples of the prior art will be hereunder explained with reference with FIG. 1 and FIG. 2.
FIG. 1 and FIG. 2 illustrate top plan views respectively of objects the defects of which are to be inspected. In the Figures, symbols S and S' generally indicate objects to be inspected. The inspected objects S in FIG. 1 contains a linear flaw or defect 1 or the like which runs at right angles to the scanning direction a of a television camera (although not shown in the drawing) which is used to pick-up the inspected object S. The inspected object S' in FIG. 2 contains a linear flaw or defect 2 or the like, which extends generally in a parallel direction with the scanning direction a of the television camera. In inspecting either of the defects 1 or 2 by the television camera, the scanning direction of the television camera is in the direction as shown by arrow a in FIG. 1 and FIG. 2. In the case of defect 1 on the inspected object S in FIG. 1, since the defect substantially crosses the scanning direction a of the television at the right angles, in the course of the television camera output, such defect 1 is easily detected by creating an irregular level at such portion corresponding to defect 1, or by the reproduction of the defect 1 on a monitor television receiver (not shown). However, since the defect 2 of the inspected object S' as shown on FIG. 2 extends in approximate parallel direction with the television camera scanning direction a, in many cases it may not be scanned by the electron beam of the television camera and accordingly appears to be extremely difficult to be detected.
It is apparent that in the real world, the defects on inspected objects be multifarious (i.e. millions) so that defects of linear nature such as defect 2 in FIG. 2 quite often exist. In other words, there are many cases that linear natured defects that extend in a parallel direction to the television camera scanning direction a do exist. In view of such actual status, the conventional systems contain a serious fault wherein in many cases such defects cannot be detected.